1. Technical Field
The present invention relates to a method of forming polysilicon, a thin film transistor (TFT) using the polysilicon, and a method of fabricating the TFT.
2. Related Art
In general, display devices, such as organic light emitting diodes (OLEDs) or liquid crystal displays (LCDs), employ thin film transistors (TFTs) as switching elements.
TFTs include a gate electrode, a source electrode, and a drain electrode wherein a semiconductor channel material layer is formed between the source electrode and the drain electrode. Channel material layers may be formed of amorphous silicon or polysilicon. Since the electron mobility of polysilicon is higher than that of amorphous silicon, polysilicon has been recently preferred as a channel material for high speed operation of TFTs.
Polysilicon is generally formed by depositing amorphous silicon on a substrate using plasma enhanced chemical vapor deposition (PECVD) and crystallizing the deposited amorphous silicon. The amorphous silicon may be crystallized by thermal annealing or eximer laser crystallization (ELC). However, since thermal annealing requires a high temperature of 600EC or more, thermal annealing is not suitable for TFTs of OLEDs or LCDs using a glass substrate. ELC can crystallize amorphous silicon at a relatively low temperature advantageously. Polysilicon crystallized at low temperature is called low temperature polysilicon (LTPS). However, ELC has a disadvantage in that, as the size of a substrate increases, crystallization uniformity decreases. Therefore, ELC is not suitable for large LCDs or OLEDs.